Most housings for electrical equipment are provided with some means to permit penetration of the housing walls for the purpose of allowing entry of electrical conductors so that the conductors can be connected to each other or to an electrical device within the housing. Because housings may be mounted in various orientations and are sometimes connected to conduit or cable approaching the housings from any of several possible directions, the housings are commonly provided with multiple access ports, usually in the form of knockouts, so that the housing can be mounted in the most convenient manner depending on the circumstances which the installer faces at the installation site.
When the housing is made to contain an electrical device which has a necessary predetermined orientation, the problem is compounded because the device and the housing must both be taken into consideration. An example of a device which has a specific installed orientation is a switchable outlet unit of the type having an outlet with a switch above the outlet. The switch cannot be below the outlet because, if it were, a cable connected to a plug inserted in the outlet could inadvertently operated the switch when the cable is moved.
Especially in the case of weather-resistant housings intended to resist water entry from rain or spray, a desirable objective is the to minimize of the number and type of penetrations of the housing walls. Water can enter a housing in a variety of ways and any penetration which is not essential for electrical purposes should be avoided. However, when the housing is to be used with an oriented apparatus, such as the switchable outlet discussed above, the housing must be capable of mounting in at least two orientations to accommodate different directions of approach of the conduit to which it will be wired. The device itself, however, has only one acceptable orientation.
A further problem with electrical equipment housings arises when the box for the equipment is non-metallic. Some provision need be made for connecting the conduit, which is usually metal, to the ground locations or terminals of the devices in the box. This ground bonding is easy and somewhat automatic with metal boxes but with non-metal boxes, special steps must be taken.